This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. I will measure energy and irradiance thresholds for inducing a change in the refractive index of micro-irradiated regions of chromosomes in mitotic PTK2 (Potorous tridactylus) kidney cells for the purpose of gaining insights into the physical mechanisms of laser ablation. I will determine the width of damaged spots for different numbers of pulses at different wavelengths. Further, for a fixed wavelength, I will measure the time required to induce a detectable change in the refractive index with varying exposure times to determine any time dependence.